According to the invention, there is provided apparatus for forming thermoplastics material elongate extrusion comprising an extruder having an extruder exit passage for extrudate; a die connected to the exit passage of the extruder through an upstream die position having an upstream portion longitudinal axis; an extrusion nozzle connected to a die downstream portion having a downstream portion longitudinal axis; handling apparatus downstream of the die for handling extrudate emerging from the die, the handling apparatus having longitudinal axis inexactly axially aligned with the extruder exit passage; the nozzle having an elongate delivery passage for the delivery of extrudate from the die to the mold tunnel; and means to adjust the position of at least the die downstream portion with respect to the extruder to provide for adjustment alignment of the die downstream longitudinal axis and the handling apparatus longitudinal axis.
Also according to the invention, there is provided an apparatus for forming thermoplastics material pipe comprising an extruder having an extruder exit passage for extrudate; a die connected to the extruder exit passage through an upstream die portion having an upstream die portion longitudinal axis; and elongate extrusion nozzle axially alignable with and connected to a die downstream portion having a downstream portion longitudinal axis; a mold tunnel having a tunnel longitudinal axis inexactly axially aligned with the extruder exit passage; the nozzle having an elongate delivery passage or annular cross section for the delivery of extrudate from the die to the mold tunnel; and adjustment means to adjust the position of at least the die downstream portion to correct any deviation from axial alignment with the mold tunnel. Suitably, apparatus for the manufacture of large diameter pipe may have a die comprising two separate portions, i.e. the die upstream portion and the die downstream portion. The die upstream portion is fixed with respect to the extruder and the die downstream portion is movable with respect to the die upstream portion. The adjustment means act between the die upstream portion and the die downstream portion to adjust the longitudinal axis of the die downstream portion to coincide with that of the mold tunnel. In this case, the die may have a housing comprising a socket part and a spigot part. The socket part may be the upstream portion which is fixed relative to the extruder and the spigot part may be the downstream portion which is adjustable in the socket part to center the longitudinal axis of the spigot portion so that it coincides with the longitudinal axis of the mold tunnel.
The inner surface of the elongate passage may be formed by a mandrel centered axially in the elongate nozzle casing through support means which allows the flow of extrudate through the die. The support means may be a spider and may be fixed or adjustable in the die. Suitably, for the manufacture of large diameter pipe the spider is fixed in the downstream portion of the die. Any adjustment of the elongate nozzle for thickness of the walls of the extrudate may be made by adjusting the position of the elongate nozzle casing with respect to the mandrel.
The extruder may be a side-feed extruder or an inline feed extruder. The adjustment means for adjusting the position of the downstream portion of the die casing with respect to the upstream portion of the die casing may suitably be adjustment screws projecting through the socket wall to adjust the position of the spigot part within it.
Alternatively, the die may comprise a one-piece die. This may be more suitable for the manufacture of small diameter pipe. In this case, the adjustment means acts between the extruder and the die rather than between two parts of a split die. Again, the adjustment means may comprise adjustment screws passing through the socket wall of an upstream socket end of the die to adjust it relative to a fixed spigot end of an extruder passage projecting into the socket.
In this case, the inner surface of the elongate passage may again be formed by a mandrel. The mandrel may, as already described, be carried on a fixed spider. Alternatively, it may be carried on an adjustable spider so that its position within the die may itself be adjustable. There is no special criterion of when an adjustable spider may be used and when a fixed spider is more suitable. However, it is commented that the fixed spider may generally be more suitable for apparatus for the manufacture of large diameter pipe.